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Re: st: adoupdate question


From   Alan Riley <ariley@stata.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: adoupdate question
Date   Mon, 29 Jun 2009 20:40:52 -0500

Richard Williams (Richard.A.Williams.5@ND.edu) asked about -adoupdate-
and ado-files downloaded from SSC for Stata 11 vs. Stata 10:
On Mon, Jun 29, 2009 at 04:06:25PM -0400, Richard Williams wrote:
> I wonder if -adoupdate- becomes potentially dangerous for people who 
> don't update their Stata version.  Suppose you have Stata 10, and you 
> have a routine you downloaded from SSC that works with Stata 
> 10.  Then, the author updates the program so it requires Stata 
> 11.  When you run -adoupdate-, won't the version that works with 
> Stata 10 get overwritten by the version that requires Stata 11?
> 
> Most authors will probably keep a renamed version of the earlier 
> program available, but it might be nice if adoupdate warned you when 
> you were about to update to a program you can't run.

It is true that -adoupdate- will seek out the newest update to
a given package which has been -net install-ed, no matter what
the version number is in the ado-files in that package.  So, Richard
is right to be thinking about this.

It would be possible to modify -adoupdate- to take note of a version
comment within the text of the package file it is checking, but even
better than that would be for this to be a feature understood by
Stata's -net- command.  It is too late for such a feature to be
added to Stata 11, but we may add it in the future.

However, Richard's email leads me to want to talk about version
control in user-written programs.  Over the years, I have seen
authors of user-written programs put out a command named, say, 'x',
which runs under Stata 11, and put out another command, say, 'x_10',
which is known to run under an earlier version of Stata.  End-users must
decide whether to install 'x.ado' or 'x_10.ado' and must remember to
type -x- or -x_10-.

There is a simple, and better, solution, for authors of user-written
programs who wish to implement version control in the way developers at
StataCorp would do so.  This solution lets users of Stata 11 type
-x- to access the Stata 11 version of x.ado, and it also lets users of
Stata 10 type -x- (NOT -x_10-) to access the Stata 10 version.

The author of the program still creates x.ado and x_10.ado, but
x.ado has a few lines of code in it which allow it to be smart
so it can call the older x_10.ado if a user is running under
version 10:

    ----x.ado--------------------------------------
    program x
        if _caller() < 11 {
            x_10 `0'
            exit
        }

        version 11
        // the code for the Stata 11 version
        // of 'x' goes here
    end
    ----x.ado--------------------------------------

    ----x_10.ado-----------------------------------
    program x_10
        version 10
        // the code for the Stata 10 version
        // of 'x' goes here
    end
    ----x_10.ado-----------------------------------


This takes no more work for an author who was going to create
both x.ado and x_10.ado anyway, but it is cleaner for end-users.
It also means that even if a user installs an updated version
of the 'x' package, as long as they have used version control in
their own do- and ado-files, the appropriate version of -x-
will be executed.


--Alan
(ariley@stata.com)
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